Furnace High Limit Switch Keeps Tripping Causes and Fixes

hello all so if you have a furnace and a high limit switch keeps tripping I thought I'd go over some of the causes and how you go about fixing it and I'm gonna put links down below for everything I'm looking at here but what is the furnace high limit switch well it's basically a safety feature that turns the furnace off when it overheats inside the furnace is a heat exchanger where all the gases and fumes are burning and the air blows past this and heats up and goes into the home and so and you never want that heat exchanger to become cracked or mixed with the air that goes into the home you want it to vent out the out the exhaust then go outside so to keep this heat exchanger from heating up and becoming too hot and cracking there's a this high limit switch will shut it down shut down the whole furnace and not allow that to happen so it's an important safety feature and a lot of people ask is can the high limit switch be bypassed and yes it can but only for troubleshooting you never want to leave this switch bypass that's that's like a major No-No because you never want that heat exchanger to become cracked because it's very dangerous if that gas mixes and gets blown into a house if there is a problem it needs to be solved and fixed and so what if some of the main causes and fixes for furnace high limit switch that keeps tripping well number one is the air filter this is very common is that you go out to a call and this air filter is just completely clogged up and no air can get by and when no air can flow by the heat exchanger it's not carrying away the heat into the home so it quickly overheats the whole furnace and the high limit switch will trip off this is very common is that the air filter is just plugged up and dirty so first thing be sure to check the air filter and be sure that it's not dirty next up would be block registers if the air is blocked from going into the home then it's going to heat up the heat exchanger too air is very important that it has to flow past that heat exchanger to cool it down or else it quickly heats up so anything blocking the airflow is going to cause the furnace to heat up so go around and check all the registers where the air blows out and be sure there's nothing blocking them like no boxes sitting on them or anything like this and be sure that's all good and next up would be the exhaust vent and with this you want to make sure that nothing's being blocked or nothing's like come apart or anything like that because if anything's blocking all the gas and everything from being vented outside then this can cause things to heat up quickly so look at the vent pipes and be sure that it all looks good it hasn't become corroded and collapsed in on itself or anything like this so number three would be exhaust fence and next up would be the a coils not all furnaces are going to have this this is for a split system air conditioning which is pretty common uh inside the bottom of the furnace will sit at eight coil and the air blows past this and during the summer this is what cools the many homes and quite commonly this becomes clogged up if the filter hasn't been changed regularly or somebody's running it without the filter for some reason then this could become really clogged up and it could block airflow from coming in and around and into the home so which will heat up the heat exchanger and causes a high limit switch to trip so take the bottom of the of the Furnace panel off and look around for the a coil and be sure that air can flow past the good if not get a brush and clean it up along with some cleaner and next up could be a possible blower motor if the if there's no air flowing because the blower motor went bad then it can cause a high limit to switch to trip so be sure that blower motor is working and blowing out correctly and next up would be the inducer motor and the inducer motor creates a pressure so that the so that the gases get vented out through the exhaust pipe and if this goes bad then the gases won't vent properly on many newer furnaces the furnace won't even start if the inducer motor goes bad because it needs to see a slight pressure and that the exhausts are being invented before the furnace even starts but number six would be a bad inducer motor and last up would be the first limit switch has just gone bad so if you checked everything else and everything else looks good you can go over and test the furnace limit switch or replace it and since it could possibly have gone bad so that's basically it I just wanted to go over some of the main causes and fixes if you have a furnace high limit switch and it keeps tripping and causing the furnace to shut down if you have anything to add please comment down below if you have any questions ask me and I'll try to answer them if this video helps you please click like please click subscribe and have a good day

Channel: HVAC Mechanic

Views: 40,775

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Id: 8pG3wasJlHs

Length: 4min 35sec (275 seconds)

Published: Fri Sep 16 2022